1. Field of the Invention
The present invention relates generally to a mobile communication system that supports an uplink packet transmission service. More particularly, the present invention relates to a method and apparatus for efficiently transmitting/receiving transmission power information and buffer state information of a user equipment.
2. Description of the Related Art
Mobile communication systems have evolved into a high-speed and high-quality 3rd generation mobile communication system for providing a data service and multimedia service in addition to a voice-oriented service. The 3rd generation mobile communication system is a mobile communication system that supports not only a voice service but also a packet service, and adopts a code division multiple access (CDMA) system. The 3rd generation mobile communication system may be classified into a 3rd Generation Project Partnership (3GPP), or Universal Mobile Telecommunication System (UMTS) that is the European and Japanese standard system based on asynchronous communication among base stations (hereinafter referred to as “Nodes B”) and a 3rd Generation Project Partnership 2 (3GPP2), or CDMA2000 that is the U.S. standard system based on synchronous communication among Nodes B.
Presently, in the 3rd generation mobile communication system that is divided into the asynchronous type (3GPP) and the synchronous type (3GPP2), standardization for a high-speed and high-quality wireless data packet service is in progress. For example, in 3GPP, standardization for a high-speed downlink packet access (HSDPA) is in progress, and in 3GPP2, a standardization work for First Evolution Data and Voice (1xEV-DV) is in progress. Such standardization results from the efforts made to find a solution for the wireless data packet transmission service of a high-speed of more than 2 Mbps and a high quality.
In 3GPP, an Enhanced Uplink Dedicated Channel (EUDCH) system has additionally been proposed as a scheme for achieving a high-speed packet transmission from a required (i.e., a Node B) to a user equipment (UE) and a high-speed packet transmission from a UE to a Node B as well.
The EUDCH system has been proposed for the purpose of further heightening the performance of the packet transmission through the introduction of a new technology in an uplink communication in an asynchronous CDMA communication system. The EUDCH system adopts an Adaptive Modulation and Coding (AMC) technique and a Hybrid Automatic Repeat Request (HARQ) technique, which have been used as the existing HSDPA technology. Accordingly, the Node B should transmit an acknowledge (ACK) or negative acknowledge (NACK) signal to the UE according to the success/failure of decoding of the received data.
However, in order to support the EUDCH, a short frame of a Transmission Time Interval (TTI) that is shorter than the TTI used in the HSDPA system to transmit packet data at high speed by rapidly indicating the state of an uplink channel. That is the EUDCH system and the HSDPA system differ from each other in terms of performing the AMC technique and the HARQ technique. The TTI can be defined in the unit of a data block in a physical channel.
Accordingly, for the EUDCH system, an uplink channel scheduling for assigning proper resources by cells should be performed together with the AMC technique, the HARQ technique and the short TTI as described above. The required uplink channel scheduling is to efficiently use the limited wireless resources.
Typically, the data rate for the uplink channel is determined by the UE within an upper threshold value of a predetermined possible data rate. The upper threshold value is provided to the UE by a radio network controller (RNC). That is, the data rate of the existing uplink channel has not been adjusted by the Node B. However, in the EUDCH, whether to transmit the uplink data, the upper threshold value of the usable data rate, etc., are determined by the Node B. Additionally, the determined information is transmitted to the UE as a scheduling command. The UE determines the data rate to be used in the EUDCH according to the scheduling command.
FIG. 1 is a diagram illustrating an example of a conventional mobile communication network in which a Node B and a plurality of UEs that perform an uplink transmission with the Node B exist.
Referring to FIG. 1, the UEs 110, 112, 114 and 116 are transmitting packet data with different transmission powers 120, 122, 124 and 126, respectively, according to the distances between the UEs and the Node B 100. The UE 110 that is farthest apart from the Node B transmits the packet data with the highest transmission power 120. The UE 114 that is nearest to the Node B 100 transmits the packet data with the lowest transmission power 124. According to a scheduling algorithm applied to the Node B 100, the transmission powers and packet data rates applied to the UEs 110, 112, 114 and 116 may be different from one another.
FIG. 2 is a view illustrating a conventional signaling procedure performed between a UE and a Node B for supporting an uplink packet service.
Referring to FIG. 2, the EUDCH is set between the Node B 200 and the UE 202 at step 204. That is, the step 204 comprises a process of transmitting/receiving messages through a dedicated transport channel. Then, the UE 202 transmits data rate information, uplink channel state information, and the like to the Node B 200. The uplink channel state information comprises an uplink channel transmission power transmitted by the UE 202, a transmission power margin of the UE 202, and the like.
The Node B 200 that has received the uplink channel transmission power can estimate the uplink channel state by comparing the uplink channel transmission power and a reception power. That is, if a difference between the uplink channel transmission power and the uplink channel reception power is small, it is determined that the uplink channel state is good, while if the difference is large, it is determined that the uplink channel state is poor. In the case in which the UE 202 transmits the transmission power margin in order to estimate the uplink channel state, the Node B 200 can estimate the uplink transmission power by subtracting the transmission power margin from the possible maximum transmission power of the UE already known. The Node B 200 determines the possible maximum transmission power using the estimated channel state of the UE, the transmission power margin and the data rate information required by the UE 202.
The maximum data rate as determined above is reported to the UE 202 at step 208. The UE 202 determines the data rate of the packet data to be transmitted within the range of the reported maximum data rate. Then, the Node B 200 transmits the packet data by the determined data rate at step 210.
If the decoding of the packet data succeeds without error, the Node B 200 transmits an acknowledge (ACK) signal to the corresponding UE 202 at step 212. When the ACK signal is received, the UE 202 transmits new packet data to the Node B 200. However, if the decoding of the packet data fails, the Node B 200 transmits a negative acknowledge (NACK) signal to the UE at step 212. If the NACK signal is received, the UE 202 retransmits the packet data previously transmitted at step 210.
The uplink physical channel for the EUDCH service as described above comprises a dedicated physical data channel (DPDCH), a dedicated physical control channel (DPCCH), a high-speed dedicated physical control channel (HS-DPCCH) for the HSDPA service, a dedicated physical data channel (EU-DPDCH) for the EUDCH service, a dedicated physical control channel (EU-DPCCH), etc.
Specifically, through the EU-DPCCH, a transport format and resource indicator (E-TFRI) of the packet data transmitted to the EU-DPDCH is transmitted. Additionally, through the EU-DPCCH, transmission status information according to the packet data transmission of the UE is transmitted to the Node B. The transmission status information comprises a buffer occupancy information (BO), transmission power status information (TPS), etc.
Through the EU-DPDCH, the packet data is transmitted using the data rate determined by the scheduling information. The DPDCH supports only a Binary Phase Shift Key (BPSK) modulation system. However, in order to heighten the data rate as maintaining the number of spreading codes simultaneously transmitted, the EU-DPDCH can support Quaternary Phase Shift Keying (QPSK), 8 Phase Shift Keying (PSK), etc., in addition to the BPSK.
As described above, the Node B receives information such as BO, TPS, etc., from the UE in order to perform the scheduling operation such as the transmission timing of the EUDCH packet data, the data rate assignment, etc. In this case, it is conventional that the BO among the above-described information is reported to the Node B only in the case in which new data is produced in an EUDCH packet data buffer of the UE. By contrast, the TPS is periodically reported irrespective of the production of the new data.
Accordingly, even in the case in which the packet data to be transmitted does not exist in the EUDCH packet data buffer, the UE continuously reports the TPS, and this causes an uplink interference level to be increased. Additionally, due to the demodulation/decoding of the TPS that is periodically transmitted from the transmitter of the UE and the receiver of the Node B, unnecessary power is consumed.